How to Make Aquarium Plant Fertilizer DIY Style

Last Updated on July 27, 2021 by cmoarz

Aquarium plant fertilizer is an important part of fish tank setup, maintenance, and management when you are keeping live plants in your aquarium. Aquatic plants often can’t survive on fish waste alone and need a good aquarium fertilizer to promote strong growth and green leaves.

Learning how to make aquarium plant fertilizer yourself will save you a lot of money in the long run, and it’s super easy to do!

Let’s get started

Diy Potassium nitrate fertilizers

Things you will need to make DIY aquarium plant potassium nitrate fertilizer:

  • Potassium Nitrate KNO3 (powder)
  • 3-liter jug with cap (this fertilizer won’t need to be put in a refrigerator, but you will need a dark container, if the container is clear, keep it in a dark place).
  • Purified Distilled water
  • Gram scale
  • A large syringe
  • Airline Tubing

Step 1: Learning the calculations and how to use the specialized calculator

First, You should learn how to use the nutrient dosing calculator over at which is, in my opinion, the best calculator for our DIY aquarium fertilizers. Don’t worry, we’re going to teach you how to use it.

Calculator pre-set "My aquarium is"

First, For the “My aquarium is” sections, you’re going to want to put in 10 gallons. If your tank is bigger than this, that’s ok, But keep it at 10 gallons. The reason being, it keeps the math simple and allows us to easily dose up if needed. The double amount for 20 gallons, 4x for 40, etc.

Calculator pre-set "My fertilizers are"

Select the DIY option in the “My fertilizers are” section.

Calculator pre-set "My aquarium is"

Select KNO3 in the “I am doing with” section.

Calculator pre-set "i am dosing with"

Select the “using a solution” radio button.

Calculator pre-set "using: a solution"

Set the container size to 3000ML (3 Liters) to match our jug size. It’s important you do use a 3 liter here just to keep the ratios correct, But once you learn how this calculator works you can experiment with bigger batches.

Calculator pre-set "container size"

Set the dose size to 2ML.

Calculator pre-set "Desired dosage size in ppm"

Now choose from the drop-down menu in the “I am calculating for” section “Dose to reach a target”

Calculator pre-set "calculating for dose to reach target"

The target N03 should be set for 8 PPM as shown in the screenshot below.

Calculator pre-set "my target is 8 ppm"

and for the last section, we will just keep it at auto for rounding purposes.

Calculator pre-set "set to auto"

When you are finished, It should look something like this:

What the calculator should look like once you've added in everything

Now hit calculate and you going to be shown lots of useful information such as this chart that compares your ratios to other popular variants and the exact ratios of ingredients you will need for your fertilizer solution.

Comparable chart to other popular mixes as well as solubility levels.
The relative range for your dose of NO3
The formula the calculator will spit out
Ingredient calculations of 740.66 grams (equivalent to 36 tbsp + 0 tsp + 1/2 tsp + 1/4 tsp + 1/8 tsp + 1/32 tsp ) of KNO3 to your 3000mL dosing containe

This will give you the exact KNO3 you will need to add to your 3-liter jug to get a dosing of 2ML per 10 gallons. So if you were dosing 20 gallons, you can easily double that to 4ML. Super simple!

What you see in the above calculations is 8 ppm nitrate, and around 5 PPM of potassium.

Important note: Do not attempt to go over 8PPM with NO3, the calculator will give you warnings about solubility. You will need to adjust your recipe with solubility in mind if you intend on creating bigger batches, You can’t just concentrate it as much as you want because it simply won’t be able to dissolve into the amount of water you’ve given it at room temperature.

The solubility of NO3 at room temperature is 360.

Step 2: Weight out your ingredients

This step is super simple, take out your trust scale and get weighing based on your calculations. In our case and in the case of this article example, 740.66 grams of KNO3.

Unfortunately, some scales may be limited in how much weight you can put on at once, so you may need to do several weigh in’s to get up to the desired grammage.

Step 3: Measure out 3L of water in your jug

If your jug already has a 3L fill line, you can ignore this step, Otherwise, fill the jug with your distilled water and mark exactly where the 3L fill line will be. It’s important to be accurate.

You can dump the water aside for use in the next step.

Step 4: Add the KN03 to the empty jug

Go ahead and dump your pre-measured amounts of KNO3 into the jug. Using a funnel here definitely helps, but I still recommend pouring the contents of the container into a small cup first and then using a spoon/funnel to get it into your jug. This improves accuracy and reduces spillage.

Step 5: Add your distilled water

Pour in the distilled water you set to the side back into the container. I know it sounded counterintuitive to take it out after the measurements, but it helps with the mixing.

Fill to the fill line you created earlier.

Step 6: Shake!

Since we’re so close to max solubility already, Shaking to get everything dissolved is an important step but will take a little bit.

It’s best to shake for 1 minute, let stand for the none dissolved particles to settle, Then start shaking again for another minute. Repeat this process until there are no more undissolved particles in the water.

Once you are certain it’s all dissolved, put a label on the bottle. “KNO3 2ml/10gal = 8 mg/l”

Step 7: Dose your tank!

Now that you finished your fertilizer solution, you can dose up to 2ml per 10 gallons of water.

This is where the air tubing and syringe will come in handy.

The tubing will allow you to get the solution deep into the tank where it needs to be, and the syringe will allow you to measure the amount easily and accurately.

Dosing amounts

If you’re aiming for 8PPM you want to do it around twice a week. If you don’t notice a difference in your plants, you might up it to 3x a week. Sometimes it’s hard to see the difference if you look at your tank every day, So consider taking pictures and cataloging them. This makes spotting the differences depending on what you’re aiming for.

If you want to go after specific species better, consider doing more frequent dosings and fewer dosage amounts. There’s a lot of overlap in plants when it comes to their requirements.

Dosage varies so you may find yourself needing to increase or decrease your dosage based on the types of plants you have, plant density, the types of substrate, the types of bioloads, etc. but in general 2ml per 10 gallons should be a good starting point with this formula.

This formula is good if you have a lot of plants that eat up all the nutrient nitrates and are suffering from nitrate deficiency in the water column.

Of course, there are hundreds of other types of liquid aquarium fertilizers you can make and you may need in the future, and they all serve different purposes and the needs of your plants. Hopefully, this one helps you deal with your nitrate issues and will teach you how to make ones that are better suited for your needs with the handy calculator.

Can I Use Tap Water for DIY Aquarium Fertilizer

You could potentially use tap water if you know what’s in it. Fertilizer formulas are to be fairly strict about what goes in them, and tap water will often also contain several other things that could throw your calculations off, or worse, poison the aquarium.

Things like heavy metal can do this.

In short, it’s probably not a good idea to use tap water when mixing DIY fertilizers unless you know exactly what’s in it.

This is especially true if you are on well water, which can contain:

Heavy metals, like cadmium and mercury, can leach into well water through the ground. Chlorine and fluoride, which are added to drinking water supplies to kill bacteria and help prevent tooth decay, may also be present in well water.

Oxidized chemicals such as sulfates and nitrates can be in well water as well. And since we’re using a mixture that’s almost completely saturated in nitrates, it could throw off the balance and create excess leftover powders in the container which can burn plants.

Can You MIX Aquarium Water With Chemical Plant Fertilizer

Yes, you can use aquarium water instead of distilled water, but just like tap water, you are going to run into issues of saturation and other metals and chemicals that could cause problems. Most likely your clean aquarium water is just dechlorinated tap water after all.

I would not suggest using just the leftover water from your aquarium for mixing chemical fertilizer either, because there could still be issues as the fish waste and excess nitrates (At least in the case of our nitrate fertilizer) which will cause saturation issues.

Can Aquarium Fertilizer Cause Cloudiness

Can aquarium fertilizer cause cloudiness? On its own no, you should never need to add enough fertilizer to cause any sort of cloudiness in your tank. However, excess fertilizer coupled with light can cause an algae bloom. This is normal the first few weeks of dosing a new tank.

Doing extra water changes and scrubbing the sides of the tank down with an algae brush will fix this issue. After a while, it will stop happening altogether.

Can liquid fertilizer go bad and cause cloudy water in aquariums?

No, most liquid fertilizers do not go bad and cause cloudiness. If you are using a nitrate KNO3 (what we’re using in this article) liquid fert and you have a large amount of magnesium sulfate (MgSO4) in your tank or from another fertilizer, You might see a reaction between the 2 that can cause cloudiness.

How Long After Dechlorinating Aquarium Can You Add Fertilizer?

Dechlorinators and water conditioners take 5-10 minutes to work their magic. All things considered, you do not need dechlorinated water to add fertilizer, but waiting doesn’t hurt either.

Can You Overdose Aquarium Fertilizer

It’s a bit of a stretch to say, but technically yes you could overdose an aquarium with fertilizer. If you put in too much fertilizer it can make the tank go out of balance and there are certain things like algae and other aquatic plant life that thrive when there is too much fertilizer in your tank.

Depending on the type of fertilizer your using, It could do nothing but cause explosive growth of algae, or it could burn your plants or outright kill everything in the tank. Always dose carefully. Use and plug in your numbers to get exact dosing information to work from.

How to Add Fertilizer to Aquarium After Fish Is Added

You can safely add macronutrients fertilizer to your planted tank at any time even if fish are in the tank. You can add it to the water when you initially set up the tank or add it before adding your fish.

Simply squirt into the water column and the leaves will suck it up.

Micronutrients such as heavy metals may pose a problem depending on the type of fish in your tank.

Will Aquarium Floss Remove Liquid Fertilizer From Aquarium

Aquarium floss will not remove liquid fertilizers from aquarium water, but your active carbon filters might scoop up trace amounts of it if you use enough.

Fortunately, that’s not necessarily a bad thing and may even slowly release it over the coming weeks. Popular advice is to consider using something else than activated carbon as a filter medium.

Can I Use Fertilizer and CO2 Booster at the Same Time in My Aquarium

Yes, CO2 and fertilizers in your planted aquarium can be used at the same time. For best results, let them do their own job separately though. I would only add fertilizer when roots are already established.

I would also avoid adding too much liquid fertilizer or any traces of solid (dry) fertilizers to an aquarium with high levels of carbon dioxide as this may cause root burn which starts off as wilting leaves and ends in plant death if left unchecked.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!